Commit 8162eab2 authored by Committed by Marge Bot
Remove the GHCi debugger's panicking isUnliftedType check
The GHCi debugger has never been that robust in the face of higher-rank types, or even types that are _interally_ higher-rank, such as the types of many class methods (e.g., `fmap`). In GHC 8.2, however, things became even worse, as the debugger would start to _panic_ when a user tries passing the name of a higher-rank thing to `:print`. This all ties back to a strange `isUnliftedType` check in `Debugger` that was mysteriously added 11 years ago (in commit 4d71f5ee) with no explanation whatsoever. After some experimentation, no one is quite sure what this `isUnliftedType` check is actually accomplishing. The test suite still passes if it's removed, and I am unable to observe any differences in debugger before even with data types that _do_ have fields of unlifted types (e.g., `data T = MkT Int#`). Given that this is actively causing problems (see #14828), the prudent thing to do seems to be just removing this `isUnliftedType` check, and waiting to see if anyone shouts about it. This patch accomplishes just that. Note that this patch fix the underlying issues behind #14828, as the debugger will still print unhelpful info if you try this: ``` λ> f :: (forall a. a -> a) -> b -> b; f g x = g x λ> :print f f = (_t1::t1) ``` But fixing this will require much more work, so let's start with the simple stuff for now.
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